Lindsey Bever and Keith Coffman

Inviting Muslims to join from abroad ... Islamic State of Iraq and the Levant spokesman Omar al-Shishani, a Georgian, stands among a group of fighters as they declare the elimination of the border between Iraq and Syria. Photo: AP

Denver Federal authorities in Denver have arrested a woman accused of providing material support to Islamist insurgents fighting the governments of Syria and Iraq, and of conspiring to commit an offense against the United States, officials said Wednesday.

According to a criminal complaint filed with US District Court in Colorado, Shannon Maureen Conley, born in 1996, attended military training with the US Army Explorers earlier this year, before trying to fly to Syria to meet a co-conspirator only identified as Y.M.

Y.M., whom Conley met online last year, told her he was an active member in the insurgent group, the Islamic State of Iraq and the Levant, also known as ISIL or ISIS, which recently shortened its name to "Islamic State."

The Sunni Muslim militant group is an al Qaeda offshoot which wants to re-create a medieval-style caliphate from the Mediterranean to the Gulf and deems Shi'ite Muslims to be heretics deserving death.

Her case had been sealed until last Friday when a federal judge ordered most of the records made public. Some details, apparently including names and addresses, were redacted from the criminal complaint provided by federal officials on Wednesday.

Court documents said Conley and Y.M. shared a view of Islam "as requiring participation in violent jihad against any non-believers," and said they decided to get engaged.

Agents arrested Conley at Denver international airport in April as she prepared to board a flight to Germany, court papers said.

Before traveling to Syria, the court papers said, Conley was to obtain additional skills and training to provide support to the insurgents, and to fight herself if deemed necessary.

Authorities say the certified nurse's aide and convert to Islam underwent training at the US Army Explorers (USAE) in Texas in February.

Conley, a Muslim convert, told federal agents she wanted to utilise the American military training to launch a holy war in the Middle East. The documents state that her “legitimate targets of attack” included military facilities, government employees and public officials, the Associated Press reported.

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In an affidavit in support of the criminal complaint, a Special Deputy US Marshal assigned to an FBI Joint Terrorism Taskforce said Conley was interviewed in mid-2013 after being spotted acting oddly outside a church in Arvada, Colorado.

The church was the scene of a mass shooting in 2007, and staff became suspicious, Christian Byrne said in his document.

In a second interview in December 2013, she told FBI agents she joined USAE to be trained in military tactics and firearms, and that she "intended to use that training to go overseas to wage Jihad," the affidavit said.

"When asked if she still wanted to carry out the plans, knowing they are illegal, Conley said that she does," it said.

“Conley felt that Jihad is the only answer to correct the wrongs against the Muslim world,” according to the documents.

If convicted, Conley faces a maximum sentence of five years in prison, a $US250,000 ($266,651) fine, or both.